1. Field of the Invention
The present invention relates generally to group handover method and apparatus in a broadband wireless communication system which supports a mobile relay station. More particularly, the present invention relates to methods and apparatuses of a mobile relay station for performing handover in place of a plurality of dependent terminals and of a serving base station for performing authentication for the plurality of the terminals over a backhaul in the handover in a broadband wireless communication system.
2. Description of the Related Art
In a cellular system, to provide seamless communication of high reliability to mobile stations in a vehicle, a handover scheme of a mobile relay station is described. For example, in this scheme, a mobile relay station mounted to a fast transport means such as bus or train performs the handover in place of a plurality of terminals existing in the fast transport means and thus provides the seamless and highly reliable service to the plurality of the terminals. That is, in the cellular system, to shorten a time of the interrupted service in the handover, the mobile relay station performs the handover in place of the plurality of the terminals and merely informs the terminals of the result.
FIG. 1 illustrates a handover procedure in an 802.16j-based broadband wireless communication system which supports the mobile relay station according to a conventional method.
Referring to FIG. 1, when a handover event occurs, a Relay Station (RS) 104 covering a Mobile Station (MS)1 100 and an MS2 102 requests Media Access Control (MAC) addresses or handover identifiers of the MSs 100 and 102 by transmitting a handover request (MOB_MSHO-REQ) message to a serving Base Station (BS) 106 in step 110. The serving BS 106 transmits a handover response (MOB_BSHO-RSP) message including the MAC addresses or the handover identifiers of the MSs 100 and 102 to the mobile RS 104 in step 112.
Next, the mobile RS 104 transmits a handover indication (MOB_HO-IND) message to the serving BS 106 to disconnect from the serving BS 106 in step 114, and transmits a ranging request (RNG_REQ) message including the MAC addresses or the handover identifiers of the MSs 100 and 102 to reconfigure the connect to a target BS 108 in step 116. The target BS 108 receiving the ranging request (RNG-REQ) message generates and transmits an independent ranging response (RNG-RSP) message to the mobile RS 104 according to the MAC addresses or the handover identifiers of the MSs 100 and 102 in step 118.
Next, the mobile RS 104 transmits the ranging response message received from the target BS 108 to the MSs 100 and 102 to finish the handover procedure in steps 120 and 122.
In the above scheme, the mobile RS checks integrity of the ranging response (RNG-RSP) message received from the target BS in a MAC-Security Sublayer (SS) 201 as shown in FIG. 2, decapsulates the ranging response (RNG-RSP) message of the MSs which are encapsulated in the RNG-RSP message, and then transmits the message to the MSs. Accordingly, when the mobile RS does not have the MAC-SS, it cannot obtain the ranging response message to transmit to the MSs. When the MAC-SS is added to the mobile RS, the complexity increases.
In the meantime, when the target BS and the serving BS use different authentication keys or when the target BS and the serving BS use the same authentication key but the authentication key needs to update because the authentication key is expired before the handover procedure is completed, the MSs should hand over and be re-authenticated in the target BS, which disadvantageously increases a service interruption time. In addition, since the re-authentication should be carried out when the target BS cannot support a security algorithm used by the MS, the service interruption time increases.